The present invention relates to an inkjet recording apparatus, and particularly relates to a technique for reducing the increase in the viscosity of an ink in an ink supply tube for supplying the ink to a recording head.
In a conventional inkjet recording apparatus, there is the possibility of a phenomenon in which ejection of the ink from a nozzle may be impossible due to an increase in the viscosity of the ink or solidification of the ink caused by drying, or intrusion of foreign objects. Therefore, the conventional inkjet recording apparatus is provided with functions for maintaining and recovering the ejection function of the nozzle by forcefully ejecting or sucking the ink from the nozzle.
On the other hand, as an inkjet recording apparatus of this type, there is a known tube-supply-type inkjet recording apparatus that supplies an ink to a recording head mounted on a movable carriage from an ink cartridge fixed in the main body through a flexible ink supply tube. In such a tube-supply-type inkjet recording apparatus, it was recognized that the viscosity of the ink increases when a solvent in the ink residing in the ink supply tube permeates the ink supply tube and evaporates (see Japanese Patent Application Laid-Open No. H2-111555 (1990)).
By the way, in recent years, there are inkjet recording apparatuses having a facsimile function in addition to a printer function, such as an inkjet printer disclosed in Japanese Patent Application Laid-Open No. 2004-255861.
In a printer having such a facsimile function, in general, there is a tendency that black ink is often used and other color inks (for example, cyan; magenta and yellow) are not used as frequently as black ink because of its applications. Thus, in a tube-supply-type inkjet recording apparatus, if there is a difference in the frequency of use of inks depending on colors, an ink which is used less frequently may stay in the ink supply tube for a long time. Then, if the ink stays in a long time, the amount of the solvent evaporated from the ink increases accordingly, and the viscosity of the ink is apt to increase. Therefore, in order to maintain and recover the ejection function of the nozzle, even when an ink is not used for recording, it is necessary to forcefully discharge and discard the ink by performing a maintenance operation periodically, and the user is caused to bear an ineffective burden for the ink consumption.
In order to prevent the above-mentioned increase in the viscosity of the ink in the ink supply tube, Japanese Patent Application Laid-Open No. H2-111555 (1990) discloses a technique for reducing the evaporation of the solvent by providing the ink supply tube with a multi-layer structure.